Selective radioreceiver



May 29 1934- H. F. ELLIOTT 1,960,774

SELECTIVE RADIORECEIVER Filed Nov. so, 1927` 5 sheets-sheet 1 im mm1 lLlmlHL/wl K Hfls ATTORNEY May 29, 1934. F, ELLIQTT 1,960,774

SELECTIVE RADIORECEI'VER Filed Nov. 30, 1927 5 Sheets-Sheet 2 INVEN TOR HIS AT TO RN EY PP` PP v May 29, 1934.

H. F. ELLIOTT SELECTIVE RADIORECEIVER Filed Nov. 50, 1927 5 Sheets-Sheet 3 BY f/Wd Hls ATTORNEY May 29, 1934. H. F. ELLIOTT SELECTIVE RADIORECEIVER 5 Sheets-Sheet 4 Filed Nov. 30, 1927 Y E uff m k m T/ Nif/M Ef v m//d H 0 W n Y n B May 29, 1934. H, F ELUQTT 1,960,774

SELECTIVE RADIORECEIVER Filed Nov. 50,' 1927 5 Sheets-Sheet 5 F'IE- S'.

INVENTOR BY {nd/d HIS ATTORNEY UN/ 7 CONTROL Patented May 29, 1934 SELECTIVE RADIORECEIVER Harold F. Elliott, Palo Alto, Calif., assignor, by

mesne assignments, to Radio Corporation of America, New York, Delaware Application November 3 5 Claims.1

This application is a continuation in part of my prior applications, iiled November 27, 1926 and having Serial Number 151,134, entitled Tuning system, said application having become 5 Patent No. 1,707,948, dated April 2, 1929, and another, led June 2S, 1926, and having Serial Number 119,114, entitled High frequency tuning system, now Patent 1,880,933, dated October 4, 1932.

This invention relates to a radio receiving system, and especially to one that is provided with a plurality of tunable circuits to impart selectivity thereto.

It is now well-known that when dealing with high frequency electrical energy, the degree of response to such energy by a circuit can be very materially enhanced by tuning the circuit so that it will ybe resonant to the frequency at which the energy is transmitted. In this Way, it is not only possible to increase the response, but also to render the system selective as regards frequency. All this is well understood, and is utilized most often in connection with radio receivers, so that the signals from a plurality of stations can be Asegregated by this tuning process.

i In many instances, the mere provision'of one or two tuned circuits is insuicient to provide the desired degree of selectivity, and to overcome this effect, the advent of several stages of radio frequency amplifiers in cascade has taken place in the past few years. Each amplifier stage, besides increasing the amplitudes of the E. M. F.s received, provides in addition, `a tunable circuit; and all of the tuned circuits contribute to render the receiver a great deal more selective than when only a few tunable circuits are used.

The tuning of the circuits can be accomplished in any one of several ways. For example, a variable condenser cr a variable inductance can be incorporated in each of the circuits, and one or both of such elements can be operated until the desiredresonance is obtained. It has also been common to attempt simultaneous tuning of all of the associated tunable circuits, by providing a unit control for all of the tuning elements. For

instance, the rotors of all of the variable elements have been mounted on a common shaft, or else arranged to be moved in unison by a common motion transmitting device.

At first blush, it appears entirely feasible to 5G secure simultaneous and accurate tuning of all of the circuits in this manner. When it is considered, however', that very high frequencies are delt with, it becomes evident that 'apparently minute effects, incapable of being compensated in this manner, can have serious deleterious results N. Y., a corporation of 0, 1927, Serial No. 236,753

(Cl. Z50-40) upon the selectivity of the system. For example, slight variations from absolute uniformity of the parts making up the tuning element cause sufficient variations in distributed capacity or stray iinductance to cause a large varlaton in the resonance settings. l

Another disturbing feature is that the stray electrostatic and electromagnetic fields have necessarily no uniform variation for all of the tuning elements, as they are simultaneously moved. Thus it happens that even if exact resonance be secured simultaneously for one setting, there is no assurance that such exactitude persists for any other setting.

Some systems in the past have attempted to overcome these disadvantages of single unit control by providing supplementary controls for all but one of the units; but it is evident that in many respects this arrangement would be as bad as a series of independently controlled tuning devices. Another proposal was to design the tunable circuits so that their resonance curves are broad. This is highly objectionable, for it largely nullies the selectivity which it is aimed to secure by a succession of tuned circuits; and besides, the eiliciency of the set is very materially reduced.

The problem of accurate simultaneous tun-v ing is rendered more complex by the provision of shielding for the stages, and neutralization or stabilization of vthe .radio frequency circuits against parasitic oscillations. Under such circumstances', much of the benefits of such shielding and neutralization are lost unless tuning is accomplished with precision. Y

It is one of the objects of my invention, therefore, to make it posslble to obviate al1 these. disadvantages in a receiver, and especially to do this by the aid of a simple structure capable of ready adjustment in the factory.

It is another object of my invention to make it possible to alter existing receiving sets so that they may have the advantages hereinbefore discussed, yet with little expense.

My invention possesses many other advantages, and has other objects which maybe made more easily apparent from a considerationof a few embodiments of my invention. For this purpose I have shown several forms in detail, which illus-A trate the general principles of my invention; but

it is to be understood that this detailed descrip-V tion is not to be taken in a limiting sense, since the scope of my invention is best Adened by the appended claims; 1

Referring' to the drawings: i Figure 1 is a schematic wiring diagram illus:`

trating one form of receiving system in which my invention is inco-rporated;

Figure 2 is a vertical view, mainly in section, of a receiving set incorporating my invention;

Fig. 3 is a horizontal sectional view taken along plane 3-3 of Fig. 2; l

Fig. 4 is a topplan View of the receiver with the cover and its associated parts removed, and some of the parts broken away, in order to disclose the structure clearly;

Fig. 5 is a fragmentary top plan View of the receiver, showing the form of the dial, and its associated parts;

Fig. 6 is an enlarged detail section, taken along plane 6 6 of Fig. 4;

Fig. 7 is an enlarged detail section, taken along plane 7-7 of Fig. 4; and

Fig. 8 is a schematic Wiring diagram illustrating another form of my invention. l

In Fig. 1, I illustrate a conventional form of radio receiving system that can be made to incorporate my invention. This system is used merely as an illustration of many other forms of systems that could as readily be used. It incorporates in this instance four stages of radio frequency amplification by the aid of thermionic amplifiers, as well as a thermionic detector and two thermionic amplifiers operating at audio frequencies. The number and arrangement of stages of amplification could obviously be varied. Furthermore, I indicate a neutralizing scheme for each radio frequency stage, in order to annul substantially the effect of the parasitic capacity between the electrodes of the amplifier other two, serving as a control electrode.

tubes, and thus to ensure stable operation. The important point is thatsuch systems, of which this is typical, include variable tuning devices in some or all of the stages of radio frequency amplification, whereby selectivity is improved.

More specifically, there is indicated a conventional form of absorbing circuit, including antenna 21, inductance 22, and a ground connection 23. Coupled to the inductance 22 is a coil 24, which serves to impress upon the first radio frequency stage, E. M. F.s induced in it by the energy absorbed in the absorbing circuit. In order to amplify the signaling impulses thus received, the'amplifer tube 25 is utilized, which is in the form of a sealed vessel evacuated to a high degree,l and having therein several electrodes. One of the electrodes, such as 26, serves as a source of electrons, which flow across the tube to another electrode, such as a plate 27. In order to cause electrode 26 to emit electrons, it is made in flamentary form, and is heated by current passed through it from the source 23, such as a battery. The current can be regulated to vary the intensity of electron flow, as by rheostat 29. Furthermore, in order lthat plate 27 attract the electrons, it is kept at a` potential positive with respect to the filament 26, by the aid of a source ofuniform potential, such as battery 30. The space current (that is, the current supported by the electronic fiow in the tube space) has a completed path, from the positive terminal of battery 30, through a coil 31, plate 27, filament 26, and connection 32 back to the negative terminal of battery 30.

It is a Well-known phenomenon that the intensity of electron emission can be controlled by controlling the potential of a point in the path of the electrons, and this is usually done by the interposition of a third electrode 33 between the This control electrode is usually inthe form of. a grid.

Minute variations in the potential difference between lament 26 and grid 33 cause correspondingly larger variations in the space current and it is due to this feature that the amplification is secured. The large fluctuations in space current, passing through coil 31, vsets up large E. M. F. fluctuations utilized in succeeding stages. The E. M. F.s existing across coil 24`are therefore impressed between the grid 33 and filament 26, whereby space current iiuctuations in the output circuit of tube 27 are produced. As is customary, the filament 26 may be grounded, as indicated at 34.

In order to neutralize the effect of the capacity coupling between the plate 27 and grid 33, which coupling might otherwise cause the tube to produce undesired oscillations, I indicate a circuit ccnnecting these electrodes, and including a condenser 35 and a coil 36, coupled magnetically to coil 31 in the output circuit. It can readily be demonstrated that when such a circuit is properly designed, the E. M. F.s in the coil 31 due to the parasitic coupling, are neutralized therein; All this is well understood, and is included here merely for the purpose of completing the disclosure.

The description of the rst stage of Yamplification is now complete. In this instance, succeeding stages are inductively coupled; and for this purpose, coil 37 is coupled to coil 31, these coils "M forming an air core radio frequency transformer. This coil serves to impress an amplified E. M. F. upon the input electrodes of the succeeding amplier tube 38, the scheme of connections being substantially identical as already described in connection with tube `25. The filament is heated from the source 28, and plate voltage is secured from the battery 30, which is bridged by a radio frequency by-pass condenser 39. However, an arrangement is provided whereby the input circuit for this tube is tuned. This is accomplished by a variable condenser bridging coil 37. It is well known that when the condenser 40 and coil 37 form a tuned circuit at the frequency of reception (which means that the capacity reactance is exactly equal to the inducta-nce reactance), then the E. M. F. existing across either the coil 37 or condenser 40 is a maximum, and if the circuit is properly designed, this maximum is sharply defined, and is `very rapidly reduced even for slight departuresfrom resonance conditions. It is this feature which makes it possible, by a series of tuned circuits, to provide a high degree of selectivity. The first input stage is in this instance also shown as tuned, l'.

as by the aid of condenser bridging coil 24.

- The succeeding amplifier stages utilizing tubes 4l and 42 may be coupled in succession in a manner entirely similar to that already disclosed.

Each stage includes in its input circuit, avaridetects the signals, by causng the audio fre- .-f".

quency modulations of the radiofrequency carrier waves to replace these radio frequency waves. This. process is well-understood, and can be secured by proper choice of tube 47, and usually by providing a small condenser 48 in the grid cir- SADO -gpl

cuit. A high resistance- 49is `also :provided for assisting the.V detector action. The output for the detector stage in'thisfinstance.includes the primary 50 of an liron cored .audio' frequency transformer., the secondary 51 of `which serves to 'impress the detected Waves upon the audio .frequency amplifier stage formedbythe tube 52. Similarly, further :audio 'frequency stages maybe added, but only yone additional one 53 is indicated. This last stage has in its output circuit a trans latin'g device, such 'as phone or loud speaker 154. `Each `stage or Aradio frequency, :especially the transformer and variable condenser, is individually shielded, ina manner to Vbe hereinafter ldisclosed. i f

It is lof course, evidentV that the number of stages, as Well as the larrangement of the coupling between stages, can-be varied. .Itis sufficient for the present purpose to point lout that the system includes a plurality -of tunable circuits, `in each of which there is incorpotated a variable tuning device, exemplified Ain the present instance by condensers 55, 40, 43, 44,. and 46. These .are arranged to be controlled;simultaneously, so :as to bring all ve' tunable circuits into alinement by a common'means. Due to the high .frequencies employed, evenslight variations from simultaf neousV resonance of these circuits, causes great 'loss in selectivity. With'my arrangement it is possible to maintain all lsuch circuits in Vuniform 'resonance for their range. l

In the present instance, the receiving vapparatus, including the tubes, coils,'condensers, fand connections, are shown as housed in a box hav- 'ing a bottom 5s orig. a), sides 5v, and a @over 58. -The cover -5'8 serves fas the main support for the parts'. Aimain supporting member 59, made from sheet stamping or a casting, is fastened to the-cover 58; 4in a manner to be hereinafter described, and provides a structure below the cover upon which the condensers, :coils land tubes are supported.` `Fig .3 illustrates in a somewhat lidiagrammatic manner, a possible arrangement of Vthe elements Voir-the bottom olf-'support 59.

' Upon this support there. are `appropriately fastened, a`series of sector-shaped metallic shield- "ing cans 60, disposedin ar circle. For the sake of simplicity, but one such can is Ishown in its entirety 'in Fi'g. 2. In the present instance, there are sixcans.

one foreach of the veradio `frequency tun-ing de` vices, and-one'for the two audio frequency .amplinersA 52 and 53 and their' transformers 55". In each radio frequencyl can there is a complete radio frequency unit, such for example as tube 25,

transformer'22-24, and con`denser'i55. Since the other cans contain entirely similar elements, it is not essential' to describe them further; the :can and itsfcntents just referred to will be ldescriberli in detail and will serve a's an example of all of these cans. Theele-ments 25,'22`'24 are merely -diagrarnmaticallyfindicted, for `their structure forms nov part of'rny present invention.

Each of the variable condensers'4`0, 43,- 44, 46, and -includes a pair of'se'ts of substantially square plates, which are relatively movable so as to interleave to a greater-or lesser extent. In Fig. 3, the sets 6land`62 are AshoWnas-in the minimum setting,only the corners of the sets beingadjacent. As shown most clearly in Flg. 6; each set is fasi tened to a tube 63 vor64`, vrotatable on relatively stationary rods VA an'd, pinned to a bar 45'7 of insulation. This" .bar is supported,` on support* ing element 59 in a manner tor be hereinafter de:` scribed; The rodsj`65 and. 66 are connected by insulation strap168,.pas'sing.l lover: threaded `ends -of these rods, .and -:held in place r*by nuts `69, which .can conveniently vform the terminals of the -sets of plates 161, Ax32. ACoiled springs '70 .are Idisposed over rods *65 and "66 'tending to open one set of plates and to close the other.

It iis of .course understood that the capacity oi the condenser is varied by varying the relative positions of the plates 61, 62. "One manner in which this can be simply accomplished is .indicatedin Figs. 2, 3, and 6. An vactuating arm '7l is fastened .to tube `63, .and `a similar arm '72 is fastended to the other tube 64. Links '73 .and "74 pivotally connect respectively to these arms, the other extremities of the links being fastened to an actuator '575. One of the links passes above, and the other below the actuator, as indicated in Fig. 2'; thusreadily permitting both links to be pivoted 'on a commonpin 76.

The operation of each of the other condensers $0,411, and 46 is likewise :secured by the aid of same actuator F75, and sets of links '78, '79, 80, and v81. The actuator is in the form of a disc, rotatable about a verticalra'xis, the links ybeing connected near the edge yof the disc., as shown in Fig. 3.V These links-pass through apertures in the cans. vAs viewed in Fig. 3, a clockwise .rotation of disc "75 will cause the condensers tol close, and to increase the value of their capacities. A ycounterclockwise rotation will .have the opposite effect, the sets of plates separating. Without further description, lit is evident Athat I have provided a novel form of 'unit control, permitting ya circular arrangement of the variable tuners, the actuator for all of them being centrally located. This ,makes for compactne'ss; and since no gears or the like are used, there is 'no appreciable lost motion. Furthermore, I 'find that the tuning lcharacteristic can be made suc-h as to give substantially a straight line characteristic for the 4curve connecting the extent of rotation of disc '75 and the fre vauency of resonance. `This is due to the fact that equal increments 'of movement of disc "75 produce unequal increments of movement :of the condenser plates.

`The manner in which the disc vactuator '75 is moved will now be described. Support 59 has a large central vertical hub 82 in which is journaled a shaft 83. At the lower end of shaft 83, a boss 841s provided, over which the -disc 75 is passed. A screw 86 clamps the disc to the shaft. At the upper end of the shaft 83, there is carried integrally, a large wheel 8'7, the section of which is illustrated in "7.. This wheel has an upper flange 88 that `carries means for rotating the wheel, and thereby the shaft 483. Referring to Figs. 4 and '7, this means includes a pair Aof links 89 and 90 operating on opposite points of a diameter of `Wheel 87. Each `link carries an ear 91 pivoted on a post 92 screwed into flange 88. A spacer washer 93 separates each of the links from the flange, and

another Washer 94 is disposed over each of the ears and is held in pla-ce by `screvv 95 threaded in the post 92. The links connect, at their other ends, to opposite extremities of a bar 96 pivoted on. a pin 97, held for vexample as by driving, in a Aboss '98 on support 59. This arm is arranged to be moved by lever 99, shown as of ribbed construction., and integral with larm 96. This lever is arY ranged to be moved manually in a manner to be hereinafterdescribed. Itis sufcient for the present tonotice that as the pivot of arm 96 is back of the axis of shaft 83, the links 89 and 90 stay parallel as this arm is moved about pin 9*-7, .but they move in opposite directions longitudinally, and

Mill

thus serve to impress a torque couple onvvheel 87.

In order to provide a stop for the movement of arm 96, a boss 100 is arranged on support 59, back of the arm 96, and having faces covered with resilient material 101'in the'pathr of movement of arm 96. Furthermore; a washer 102 is disposed over the hub of arm 96 and is held in place by screw 103, whereby said arm is held against vertical displacement on pin 97.

The description of the mode of operation of the tuning elements is now complete. However, it is impossible without some such arrangement as an adjustable cam, to aline the tuning elements so that they remain exactly in step for the entire range of variation. In order to provide the compensation, the insulation bar support of each condenser is arranged to be movable. 'Considering Figs. 3, 6, and 7, it is evident that if bar 67 is moved about either of the axes of rods or 66, the relative positions' of the condenser plates will be correspondingly varied, entirely independently 'of the movementof links 73 and 74. 'l Only a slight compensating movement of this bar 67 is necessary to keep the elements alined, but such movement should be adjustable over the entire range of lvariation of condensers 40, 43, 44,46, and 55. It is nowto be noted that disc moves only a small portion of a complete revolution to operate the condensers from minimum to maximum capacity. Thus it is possible to support an adjustable cam structure on wheel 87, which has separate cam portions serving to operate bars 67 independently of each other.. In the rst place, each bar 67 is supported on rod 65 which passes through a stationary bushing 103 forming a bearing, in boss 104. Anarm 105 is fastened to shaft or rod Y65,`at the other end of which a-cam follower roller 106 is pivoted. It is evident that acam, acting on roller 106 will serve to move support 67 about the axis of rod 65. A spring 107 is fastened at one end to support 59, and at. the other end, to bar 67, whereby the rod 65 and its associated parts are urged in .a direction to cause roller -106 to engage the cam surface. Y

This cam surface itself is adjustable, and comprises one or more strips .108 of` flexible material, such as sheet copper or bronze. It is accommodated in a groove'109 in the periphery of wheel 87 (Fig. 7) and it extends angularly a sufficient distance to affect all five of the followers 106 for the full angular movement of wheel 87. Thus strip 108 'serves as a plurality of cams.` The ends of the strip are connected by a tension spring 110 (Fig. 4). The radial position of each portion of the strip is adjustable by the aid of a plurality of adjusting set screws. 111 set in the rimf wheel 87, preferably at an angle to permit ready insertion of a screw driver blade. Each of these screws has a round point contactingwiththe inner surface of the strip 108. In this way; relative movement between the screws and the strip.108 longitudinally of the stripv is permitted, to Vform a smooth, continuous surface.

t is evident that' by proper adjustment of those screws 111 which are immediately under the cam rollers 106 at any point of the range of movement of wheel 87, the rods 65 canall be moved slightly so as to bring all the tuned circuits into resonance. 'One cam structure forming, however, a pluralityo'f cam surfaces, is all that is needed; and this structure is substantially round'render-. ing it easy and inexpensive to manufacture. The screws 111 are set close enough together to ensure 'complete accuracy for the entire range of tuning. The method of adjustment involves merely positioning the wheel 87fsuccessively'so that the followers 106 are immediately over certain screws 111; and at each of these positions, these certain screws are carefully adjusted to bring all the condensers into alinement.

The supporting member 59 is provided with an inner flange 112and an outer flange 113, forming an annular space for accommodating the wiring, fixed condensers, and other elements needed in thesystem. A cover plate 114 is shown for this space in Fig. 2, but for the sake of clearness, is omitted in ;Fig.v 4. Furthermore, adjacent the left hand portion of support 59, there is an extension 115 upon which is supported a terminal block 116, exposed through a window 117 for permitting connections to be made to the batteries, loud speaker, or other external elements.

The supporting member 59 is fastened to the cover 58 by severalscrews, such as 118. One of these passes-into boss 100; and the others pass through a dial plate 119 (Figs. 2 and 5) and into bossesy 1 20which are formed on support 59 and extend upwardly to cover 58.

There remains to be described, the dial arrangement for indicating the setting of the apparatus. The dial plate 119 has an arcuate aperture, defined by the inner surface 121 of the rib on saidplate. This plate covers a substantially coextensive aperture 122 in cover 58. Through aperture 121 can be sighted a scale 123 on a member=124 fastened on the bottom of cover 58. This scale can include a frequency scale 125, a wave length scale 126, and .a clear space between these scales upon whichstation call letters can be written. A transparent pointer or indicator 127 is arranged to sweep over these scales as the tuner is operated. It has a main slot 128 and narrow end slots 129, the former for permitting call letters to be written on scale ,123, and the latter for permitting a short mark to be drawn corresponding to these letters.v To obtain any such setting marked as thus described, it is merely necessary to bring indicator 127 in such position that the narrow slot just exposes the mark.

The indicator 127 is of course carried by arm 99, so that as -this arm is moved, the indicator moves also.` This indicator is fastened, as by a pair of screws 13 0, to a boss 131 at the free extremity of vlever 99.. This boss 131 extends into aperture 122 and past the edge of member 124, so that its top surface is just slightly above the scale 123.. In order to provide a manual control of lever- 99,.so as to make it possible to provide for a fine adjustment, as by reduction gearing, a knob 132 is provided, carried by arm 99 in a manner now tto be described. A shaft 133 passes through a large clearance aperture 134 in the end of arm 99, and is pivoted at its bottomby the aid of pin 135. This shaft carries an extension 136 on which is journaled a tube 137, having teeth meshing with teeth 138 on the larger arcuate edge of plate 119. This tube is held against vertical displacement by washer 139 riveted over the end of extension 136. Knob 132 passes over tube 137 and is tightened in place thereon byset screw 140. It is evident that by moving shaft 133 on its pivot 135 away from the teeth 138 by the aid of knob 132, tube 137 canbeV disengaged from the. edge of aperture 121 ...and lever 99 can be quickly moved to any desiredv point.v A ilat spring -141 resiliently urges shaft 133 to engaging position. After this coarse adjustment is effected, the spring 141 can be allowedtoreturn shaft 133 to the position indicated, and the knob can then be turned, to cause tube'137 to move along the stationary edge. of

aperture 121 in order to procure a fine adjustment. Of course if tube 137 be made from proper material, merely a frictional engagement, without teeth, could be relied on for the ne adjustment of lever 99. Furthermore, it is entirely feasible then to make shaft 133 rigid and without pivot 135 or spring 141. Under such circumstances, the coarse adjustment can be effected by grasping knob 132, and moving it without rotating it, in the arc prescribed by the axis of arm 99, the smooth outer surface of tube 137 slipping along the edge of the aperture. For fine adjustment, the knob can be turned, providing a friction gear movement.

One or more small incandescent lamps 142 can be provided on member 124 to illuminate the scale, and can be hidden by dial plate 119.

It will be noted in Fig. 5 that the wave length scale is proportional; and by proper design of links 73, 74, either this scale or the frequency scale can be made proportional. This function is due to the particular mechanism used for setting the condensers, and especially to the use of the link system that causes the condenser setting to be unequal for equal settings of actuator arm 99.

Of course other kinds of receiving systems can employ my unit control. For example, in Fig. 8 I illustrate a superheterodyne system of reception, in which a tuned loop circuit is used as an absorbing circuit. The loop 142 is tuned by a variable condenser 143, across which is connected the input electrodes of a radio frequency amplifier 144. The output circuit of this amplii-ler is coupled to a tunable circuit 145, having the variable condenser 146. In order to provide a fixed intermediate frequency, oscillations are caused to combine with the oscillations in this circuit, to give the desired beat frequency. In this instance, a tube 147 serves to generate oscillations, its output circuit having a coil 148 serving to feed back energy into the input circuit, and thereby sustaining oscillations. This coupling is effected by the aid of a coil 149 in the input circuit, which is also coupled to the coil 150 in the input circuit of a detector tube 151. The variable condenser 152 provides a tuning means for the oscillator, and thus todetermine the frequency of the oscillations produced thereby.

The input of detector 151 is influenced by both the received oscillations and the locally generated oscillations. A grid bias battery 153 and by-pass condenser 154 therefor can also be provided in the detector circuit. The output circuit for the detector is coupled in any wellknown mannerA to a fixed tuned circuit 155, the frequency of tuning being that of the beat frequency detected by tube 151, and having a value intermediate that of audibility and that received by the absorbing circuit. Two intermediate frequency stages are indicated, including the amplifier tubes 156 and 157; thence the impulses are detected to audio frequency in a regenerative detector 158, and can be passed on to one or more audio frequency stages such as 159; finally the last output circuit includes a translating device, such as phone or loud speaker 160.

The superheterodyne is operated to produce a constant intermediate frequency which makes it possible to set the intermediate frequency amplier stages accurately and permanently at the desired resonance point. However, it is necessary to vary the tuning of the absorbing circuit and of the oscillation circuit as the frequency of reception is varied. This is accomplished by the condensers 143, 146, and 152. These tuning elements are indicated as moved by a unit control, which is so arranged that the respective circuits have the proper relative frequencies at all times. Thus the superheterodyne can be made a truly one dial system.

I claim:

1. In a radio receiver, the combination of a plurality of cooperating tunable circuits, a tuning element for each of said circuits, a single movable control means for adjusting said tuning elements in unison, a movable supporting means for each of said tuning elements, and additional means operating in unison with said single control means and individually adjustable with respect to each of said supporting means throughout the range of movement of said control means for moving said supporting means to impart supplementary precise adjustment of said tuning elements, said additional means including a member providing a continuous annular cam surface deformable in zones corresponding to said condensers.

2. In a radio receiver. the combination of a plurality of cooperating tunable circuits, a variable condenser for tuning each circuit, a common actuator for said variable condensers, means for imparting supplementary precise adjustment to each of said variable condensers, said last named means including a movable support for each of said condensers, and a single adjustable cam means operated by said common actuator to move said supports thereby to actuate said supplementary adjustment means, said cam means providing a single annular surface adjustable in Zones.

3. In combination, a plurality of amplifying circuits in cascade, a plurality of condensers one in each of said circuits and individually variable, a unitary control means for varying the capacities of said condensers, means including a single cam surface variable individually with respect to each condenser arranged for simultaneous operation with said unitary control means, and means for individually varying said surface with respect to each condenser.

4. In combination, a plurality of amplifying circuits in cascade, a plurality of condensers variable as to capacity and each in one of said circuits, means for varying the capacities of the several condensers simultaneously and means for Varying said condensers in individually variable degrees including a single rotatable member having a single cam surface adjustable individually with respect to the control of each condenser and operable simultaneously therewith.

5. In combination, a plurality of amplifying circuits in cascade, a plurality of condensers variable as to capacity, each of said circuits including one of said condensers, means for varying the capacities of the several condensers simultaneously and means for varying said condenser in individually variable degrees including a single rotatable member having a single cam surface adjustable individually with respect to the control of each condenser and throughout the range of capacity changes of each of said condensers.

HAROLD F. ELLIOTT. 

